Polymorphonuclear leukocytes (neutrophils) are specialized cytotoxic cells that provide host defense against bacteria, fungi, and viruses. Recent evidence suggests that neutrophils also participate in cytotoxic reactions against neoplastic cells. Neutrophil cytotoxicity involves several mechanisms that are independently controlled and regulated through cell membrane receptors. Lymphocytes produce humoral mediators that may regulate these cytotoxic mechanisms. We recently described a newly recognized T-lymphocyte product that inhibits the migration of human neutrophils (NIF-T). We purified NIF-T by antibody affinity chromatography and determined its subunit structure. We also demonstrated that human neutrophils have specific binding sites for NIF-T. During the past year, we have purified NIF-T to homogeneity by reverse phase high performance liquid chromatography (HPLC). NIF-T biological activity was recovered from a single HPLC fraction (titers of 1:64,000) as well as from SDS-PAGE. The correspondence of a single protein with substantial biological activity confirms the identification of NIF-T. In addition, partial amino acid sequencing has been obtained to confirm the purification of NIF-T to homogeneity. From partial amino acid sequences, oligonucleotide probes will be obtained. We will utilize these probes to clone the gene for NIF-T. Moreover, we can now begin functional studies of NIF-T on neutrophil oxidative metabolism. Homogeneous NIF-T will be used to obtain monospecific antibodies to NIF-T, either monoclonal from mouse hybrids or polyclonal from rabbits. Purifying NIF-T to homogeneity will enable us to achieve our long-term goal of studying the molecular biology of NIF-T and assessing its clinical therapeutic potential. (LB)